1. Field of the Invention
The present invention relates to an organic semiconductor material having rodlike low-molecular weight liquid crystallinity with unique charge transfer characteristics.
2. Background Art
In 1993, triphenylene derivatives among representative materials of discotic liquid crystals have been found to have a high-speed charge transport capability which is 103 to 104 times higher than the charge transport speed of amorphous organic semiconductors which have been put to practical use in, for example, photoconductor drums for electrophotography and organic EL devices. Further, two years after the finding, rodlike smectic liquid crystals, which have been considered as an ion conductor up to that time, have also been found to have high-speed electron conductivity which is superior to the charge transport capability of the triphenylene derivatives. The above finding has led to gradual recognition that liquid crystalline materials are to be placed as new high-quality organic semiconductor materials having spontaneous molecular orientation capability.
It has been observed that these liquid crystalline materials have a mobility of more than 10−2 cm2/Vs which is very large as an organic material although the mobility is still about one order of magnitude smaller than that of crystalline materials. Further, it has been clarified that the behavior of these liquid crystalline materials is different from that of conventional solid materials, for example, in that, unlike conventional amorphous materials, the mobility does not depend upon the temperature and the electric field and in that, in a polydomain structure (corresponding to “polycrystal” in the crystal), unlike polycrystalline materials, domain interfaces are electrically inert.
The properties of these liquid crystalline materials are considered attributable to molecular orientation similar to that of crystals and fluidity similar to that of liquids, which are characteristic of liquid crystalline materials. By virtue of these properties unique to the liquid crystalline materials, the liquid crystalline materials are expected to be applied to various applications which include, for example, thin-film transistors (known also as “organic TFT”) utilizing a liquid crystalline material as an organic semiconductor material, luminescent elements, and solar batteries. For example, Japanese Patent Laid-Open No. 312711/1998 discloses a liquid crystalline organic semiconductor material having a high level of charge mobility.